Timer accuracy precision

Hi,

I need a precision timeout functionality. Like several months.

I have used an app_easy_timer() with longest delay possible (5*6000-1), which is 5 minutes -10ms. Correct me if am wrong.
In my timer callback I increment my own counter and restarts the timer with app_easy_timer().
To get the highest precision I use
#define CFG_LP_CLK LP_CLK_XTAL32
XTAL32睡眠。
However, it looks to me like my timer is running 5% to fast.